Thiocubane clusters containing a homometallic core M.sub.4 S.sub.4 are known in the art. The thiocubane core is so-named because of its molecular architecture, i.e., two tetrahedra of metal and sulfur atoms interlock so that the metal atoms and bridging sulfurs occupy the alternate corners of a distorted or approximate cube. Homometallic thiocubane structures containing, e.g., Co, Fe, Mo, have been synthesized and discussed at length in the chemical literature. See, e.g., Mak et al, Angew. Chem. Int. Ed. Engl. 23 (1984), pp. 391-2; shibahara et al, J. Am. Chem. Soc. (1984), 106, pp. 789-791; Chu et al, J. Am. Chem. Soc. (1982), v. 104, pp. 3409-3422 (and references cited therein) and Simon et al, J. Am. Chem. Soc. (1973), v. 95, pp. 2164-2174.
Compositions containing heterometallic thiocubane clusters have also been studied. The particular interest in the Fe.sub.2 MoS.sub.4 cluster, because of its possible function as the biologically active part of nitrogenase, has led to the attempted synthesis of other similar compositions. See, e.g., Curtis et al, Inorg. Chem., v. 22, pp. 2661-2; Brunner et al, Agnew. Chem. Int. Ed. Engl 22 (1983), pg. 549; Brunner et al, J. Organometallic Chem., 240 (1982) C41-C44; Holm, Chem. Soc. Rev. (1981), v. 10, p. 455; and Armstrong et al., Inorg. Chem. (1982) v. 21, 1699-1701.
In addition to the interest shown in the bimetallic thiocubane cluster as a biologically active enzyme constituent, others have suggested that sulfided clusters containing molybdenum and a Group VIII metal, e.g., Fe, Co or Ni, may be useful as models in clarifying the somewhat poorly understood activity of hydrodesulfurization catalysts based on "sulfided" iron, cobalt, or nickel molybdates and tungstates on oxide supports. See, Curtis et al, supra, and the references cited therein; Gates et al, "Chemistry of Catalytic Processes", McGraw-Hill, New York (1979), pp. 390-445.
In the earlier syntheses of the thiocubane core, the approach was typically "spontaneous assembly". See, Holm, supra. Later work in homometallic transition metal sulfide chemistry led to smaller clusters which could be considered fragments of the thiocubane unit. These fragments, e.g., Cp.sub.2 M.sub.2 S.sub.4 and related compounds (where Cp represents the cylcopentadienyl ligand), are potential building blocks for heteronuclear thiocubane clusters and can be used to form clusters with M.sub.2 M.sub.2 '(.mu..sup.3 -S).sub.4 cores. See, the two Brunner et al articles, supra.
None of the prior art shows the synthesis of M.sub.2.sup.1 M.sub.2.sup.2 (.mu..sup.3 -S).sub.4 L.sub.2.sup.1 L.sub.2.sup.2 L.sub.2.sup.3 where M.sup.1 is Re, V, Mo or W, M.sup.2 is Co, Cr, Cu, Ni or Fe, L.sup.1 is a bidentate sulfur and/or nitrogen bearing ligand, and L.sup.2 is optional but may be an S, N, P, or O monodentate donor ligand, e.g., a solvent or other Lewis base molecule, and L.sup.3 may be CO, a monodentate anion ligand such as a halide (preferably Cl), mercaptide or alkoxide, or another O, N, P, or S containing monodentate donor ligand.